fsal-proxy: fix NFS4ERR_BAD_SEQID in pxy_create()

As ffilz pointed out long time ago in
http://sourceforge.net/p/nfs-ganesha/mailman/message/30876823,
pxy_create() mistakes stateid->seqid for open owner seqid and causes
NFS4ERR_BAD_SEQID errors.

This patch maintains an open owner seqid in the client side (proxy FSAL in this
case), and increments the open owner seqid upon state mutating operations
(OPEN, OPEN_CONFIRM, and CLOSE).

Signed-off-by: Ming Chen <mchen@cs.stonybrook.edu>